This invention relates to an apparatus for determining a representative spring constant of a golf club head.
Appendix II, 5a of the Rules of Golf reads that the material and construction of, or any treatment to, the face or clubhead shall not have the effect at impact of a spring (test on file), or, in part, significantly more spin to the ball than a standard steel face, or have any other effect which would unduly influence the movement of the ball and, further, that the face of the club shall be hard and rigid (some exceptions may be made for putters) and, except for such markings listed below, shall be smooth and shall not have any degree of concavity.
Heretofore, various techniques have been employed to determine the effect at impact of a golf club head on a ball. One such procedure has been published by the United States Golf Association, Procedure for Measuring the Velocity Ratio of a Club Head for Conformance to Rule 5a, Appendix II, Revision 2, Feb. 8, 1999. This procedure, however, requires several steps and is relatively time consuming.
It is an object of this invention to simplify the test for determining the flexibility of a golf club head and in particular to measure a representative spring constant for a golf club head.
It is another object of the invention to determine a spring constant that is representative of the flexibility of a golf club head when impacted on the usual striking face.
It is another object of the invention to reduce the cost of testing to determine the flexibility of a golf club head.
It is another object of the invention to reduce the time required to perform a test for determining the flexibility of a golf clubhead.
It is another object of the invention to provide a portable apparatus for determining the flexibility of a golf club head.
Briefly, the invention provides an apparatus for estimating the flexibility of a golf club head.
The apparatus is comprised of a mass of material which is mounted at a fixed point and means for suspending a golf club having a head thereon from a fixed pivot point with the head disposed in opposition to the mass of material for freely pivoting of the golf club about the pivot point to impact the head against the mass of material. In addition, a means is provided for recording an acceleration in movement of the material mass from the fixed point in response to an impact of the golf club head on the mass and for calculating a velocity history of the material mass over time.
In one embodiment, the means for recording the acceleration of the material mass and calculating the velocity history includes an accelerometer which is connected to the mass for producing a voltage signal in dependence on the acceleration of the mass from the fixed point after being struck by the golf club head as well as an oscilloscope which is connected to the accelerometer to receive and record the voltage signal and to calculate the velocity history.
In another embodiment, a laser may be employed to detect the acceleration or velocity of the mass of material. For example, a laser may be used to determine the distance from the laser to the mass of material, e.g. a steel ball mounted on a shaft in a cantilevered manner, by determining the time that a pulse of light takes to reach the ball from the laser and bounce back to the laser. If this is done many times, the distances can be differentiated to calculate velocity and acceleration of the ball. Another embodiment could involve the use of a strain gauge on the shaft of the cantilevered ball.
As a matter of convenience, the apparatus includes a means for releasably holding the suspended golf club in a loading position with the head spaced from the mass of material. Once released, the golf club is free to pivot thereby allowing the head to move from a loading position against the material mass, for example, to fall in pendulum-like fashion into the mass of material.
In one embodiment, the apparatus includes a mounting block and a vertically upstanding column on a mounting block to support the mass of material thereon in a fixedly mounted manner. In this embodiment, the mass of material is made of steel of spherical shape.
The method provided by the invention allows for mounting the mass of material at a fixed point and of suspending the golf club from a fixed point with the head disposed in opposition to the mass of material for freely pivoting of the golf club to impact the head against the mass of material. In accordance with the method, the golf club is pivoted into a position to space the head from the mass of material and thereafter, the golf club is released to pivot under gravity to impact the head against the mass of material.
In accordance with the method, an acceleration of the mass of material is recorded during movement from the fixed point in response to the impact of the golf club head and a velocity history of the mass is calculated over time.
The recording and calculating steps are carried out by an oscilloscope or any other suitable means.
Further, in accordance with the method, the time at which the calculated velocity is at a maximum is determined. This time corresponds to the time at which the recorded acceleration is zero.
The method steps are repeated, for example, ten times, to obtain an average time (tz). Thereafter, the representative spring constant (Kc) of the golf club head is estimated using the equation: Kc=0.2971xc3x97tzxe2x88x922.15570 where tz is the characteristic time in seconds and Kc is the representative spring constant in N/m. Other forms of equations would be suitable.